<!DOCTYPE html>
<html lang="en">
  <head>
    <meta charset="UTF-8" />
    <meta name="viewport" content="width=device-width, initial-scale=1.0" />
    <title>Document</title>
  </head>
  <body>
    <script>
      var a1 = prompt('今天几号');
      if (a1 % 7 === 1) {
        console.log(alert('星期三'));
      } else if (a1 % 7 === 2) {
        console.log(alert('星期四'));
      } else if (a1 % 7 === 3) {
        console.log(alert('星期五'));
      } else if (a1 % 7 === 4) {
        console.log(alert('星期六'));
      } else if (a1 % 7 === 5) {
        console.log(alert('星期天'));
      } else if (a1 % 7 === 6) {
        console.log(alert('星期一'));
      } else if (a1 % 7 === 0) {
        console.log(alert('星期二'));
      }
    </script>
  </body>
</html>
